Galvanizing preflux wash composition

ABSTRACT

AN AQUEOUS PREFLUX WASH HAVING THE PURPOSE OF WETTING A FERROUS METAL WITH A FILM TO CONDITION THE SURFACE IN FINAL PREPARATION FOR NON-FUMING GALVANIZING IN A MOLTEN ZINC BATH USING A SMOKELESS BLANKET FLUX ACCORDING TO MY PAT. NO. 3,244,551. THE PURPOSE OF THIS PREFLUX IS NOT ONLY TO REPLACE THE CONVENTIONAL ZINC AMMONIUM CHLORIDE CONTAINING PREFLUX MATERIAL, WHICH IS FUMING, BUT TO ELIMINATE ALL FACTORS CONTRIBUTING TO AIR POLLUTION.

Uni'ted States Patent "ice 3,740,275 GALVANIZING PREFLUX WASHCOMPOSITION Sidney M. Heins, Chicago, Ill., assignor to ThiemCorporation, Milwaukee, Wis.

No Drawing. Continuation-impart of application Ser. No. 128,551, Mar.26, 1971. This application Aug. 6, 1971, Ser. No. 169,846

Int. Cl. B23r 35/34; C2211 9/10; B32b 15/18 U.S. Cl. 148-26 ClaimsABSTRACT OF THE DISCLOSURE An aqueous preflux wash having the purpose ofwetting a ferrous metal with a film to condition the surface in finalpreparation for non-fuming galvanizing in a molten zinc bath using asmokeless blanket flux according to my Pat. No. 3,244,551. The purposeof this preflux is not only to replace the conventional zinc ammoniumchloride containing preflux material, which is fuming, but to eliminateall factors contributing to air pollution.

RELATED APPLICATION The related application pertaining to this inventionis Ser. No. 128,551, field Mar. 26, 1971, of which the instantapplication is a continuation-in-part.

BACKGROUND OF THE INVENTION In the galvanizing of ferrous base metal,the essential function of a blanket flux is to prepare the surface ofthe metal by cleansing it of rust and other corrosion products bychemical means. Only metallically bright surfaces, i.e., those free fromall non-metallic substances, can react with each other. The base metalpresumably has already been degreased and pickled removing dirt, grease,scale layers and iron salt residues by conventional means. The main taskof the blanket flux is to remove all impurities from the iron surface,as well as to keep free from oxides that part of the zinc bath surfaceat which the steel is immersed into the bath. The impurities on thesteel surfaces are partly those scale components which have not beendissolved by the acid of the pickling bath, such as complex iron oxides,or inclusions in the iron, sparingly soluble in acid, such as Fe C andpartly the reaction products of the pickling process, i.e., aqueoussolutions of iron chlorides or iron sulphates. One source of thesesurface impurities occurs while the articles to be galvanized are beingtaken from the pickling bath to the galvanizing bath, wherein ironsurfaces are exposed to the action of the atmosphere, and these ironsalts become oxidized. The purpose of the blanket flux is not only toremove these actual iron salts from the ferrous metal surface itself butalso the water adhering to the articles. On the zinc bath surfaceitself, it is also necessary for the blanket flux to take up the oxidesof the zinc bath formed by the action of oxygen, the flux being requiredto shield the place of immersion in such a manner that during the firstreaction between iron and zinc, all oxygen is kept away from the tworeactants.

It is, therefore, necessary for the flux to be able to wet the twometallic surfaces satisfactorily and remove everything that may find itsway in between them. By removing all foreign bodies from between the twometals, these 3,740,275 Patented June 19, 1973 can be brought so closeto each other that they can approach within reach of their metallicactive forces. In the process known as wet-galvanizing, the flux isplaced as a blanket onto the zinc bath so that the wet iron objects froma prewash procedure are immersed into the molten metal bath through themelted flux blanket. In the process referred to as drygalvanizing, apreflux material is first applied to the galvanzing articles as anaqueous solution after which it is allowed to dry before immersion ofthe articles through a flux blanket into the zinc bath as before.

It is a common practice in preparation for galvanizing that afterpickling, the articles are washed in cold for warm water. 'On the Way tothe galvanizing tank, these moist surfaces, which have become veryactive by pickling, are exposed to the air. However carefully washed,some iron salts still remain behind in the aqueous washing material andon the iron surface where they are rapidly converted by air into basiciron salts. In recent years, a liquid preflux wash has been used todetach these basic iron salts from the iron surface and simultaneouslyto act as a flux in the manner described for dry-galvanizing. By thusbeing covered, the iron surface is protected against oxidation on theway to galvanizing without attack on the iron base and the amount ofdross formed in the galvanizing bath is reduced.

At the present time, the galvanizing trade is using a mixture of zincchloride (ZnCl and ammonium chloride (NH Cl), or zinc ammonium chloride(ZnCl -2NH Cl or ZnCl -3NH Cl) as a preflux wash for the purpose ofwetting the ferrous base metal with a film to condition the surface inpreparation for galvanizing in the molten metal bath. This perflux washcauses visible smoke-like fumes to develop when carried over in the bathin a manner characteristic of all ammoniacal salt fluxes.

Because all ammoniacal salt preflux washes cause visible smoke fumes todevelop even when carried over into a molten zinc bath using a smokelessblanket flux according to my Pat. No. 3,244,551, there is a standingneed for a preflux wash which is non-fuming when used in conjunctionwith my smokeless blanket flux.

SUMMARY OF THE INVENTION The primary object of this invention is airpollution control. The emission of fumes and visible smoke from the zincpots of galvanizing baths has always contributed to undesirablepollution of air in shop and factory. It is the purpose of thisinvention to render the whole galvanizing process completely free ofsuch obnoxious smoke and fumes.

While a smokeless galvanizing flux such as described in my Pat. No.3,244,551, used as a blanket flux in the wet process, does not emit anyfumes, it is a contributing object of this invention to provide anon-fuming preflux wash which, if used in connection with adry-galvanizing" application, also results in a non-fuming operation.Such preflux washes are in general made smokeless by replacing theconventional ammoniacal fluxes used in the galvanizing trade with anon-ammoniacal flux which does not fume.

The preflux wash composition of this invention is comprised basically ofa mixture of about 60% zinc chloride, about 15% borax or boric acid,about 5% potassium aluminum fluoride, about 10% sodium chloride andabout 10% of either barium chloride crystals or calcium chloridepellets. Normally these preflux washes are of a sufficient strength whendissolved in water to provide a solution of about 15 to 50 B. and areused at a temperature of around 150 to 180 F.

The non-fuming preflux wash process used in preparation of the iron orsteel surfaces after pickling comprises the steps of washingthe surfacesin cold or warm water and then immediately immersing these surfaces inthe preflux Wash composition of this invention and Withdrawing the sameafter said surfaces have been fully wetted with the said composition anda film of the composition is firmly attached thereto.

DESCRIPTION OF THE INVENTION Broadly the preflux composition of thisinvention is comprised of the following ingredients in terms ofpercentages by weight:

Ingredients: Percent by weight (range) Zinc chloride 35-75 Borax orboric acid 5-l5 Potassium aluminum fluoride 510 Sodium chloride 20Barium chloride, calcium chloride 10-20 The borax and the boric acid areinterchangeable With each other. The boric acid with a more acid bathgives slightly better results. The barium chloride and the calciumchloride are interchangeable with each other or alternately may bemixtures of any one or both of these salts.

Any preflux wash composition within the above specified proportionallimits and having a solubility strength in Water of about to B. and whenused at a temperature of around 150 to 180 F. for light gauge articleswill produce excellent fluxing properties when used in conjunction withsmokeless blanket flux pursuant to the disclosure of my Pat. No.3,244,551. However, heavy gauge articles require a somewhat higher B.

The function of each of the above mentioned ingredients other than toprovide a non-fuming or non-smoking preflux Wash composition is not toowell understood. It is believed, however, that the zinc chloride acts asa cleansing agent while the borax or boric acid will absorb the ironoxides. The potassium aluminum fluoride improves fluidity or lowers theviscosity of the molten flux composition. The fluoride salt is alsobelieved to assist in preventing the zinc chloride from decomposing orconverting to other zinc compounds (e.g., hydrate or oxide) such as, forexample, by reaction with atmospheric constituents. In addition, thefluoride salt is believed to act between the base metal and the moltenmetal of the galvanizing bath to result in a more firm adherence of auniform metallic coating; and to prevent oxidation of aluminum metal, ifany, in the molten zinc metal bath. The sodium chloride and thealternates, barium chloride and calcium chloride, are believed to assistin the obtaining of a true solution of the composition in the moltenstate or liquid phase.

The above mentioned proportional limits should be substantially adheredto because compositions outside these ranges have solubilities in wateroutside the range of 15 to 50 B. resulting in a deficiency of one ormore of the above discussed functions of the specific ingredients. Thus,in order to obtain satisfactory results, the proportional limits of eachingredient should be adhered to in accordance with the above statedlimits.

From my experiments, it appears that the presence of potassium andfluorine are essential in this invention and may not be substituted.Apparently the combination of elements present produces a synergisticeffect in improved fluxing properties while fluoride emission was keptbelow 28 parts per million.

The preferred composition of the preflux wash of this invention is inaccordance with the following proportions of ingredients in terms ofpercentages by Weight:

Ingredients: Percent by weight Zinc chloride 6-0 Borax or boric acid 15Potassium aluminum fluoride 5 Sodium chloride 10 Barium chloride,calcium chloride 10 The above ingredients dissolved in water in thestated proportions give a preflux wash solution having a strength of 18B. When heated to F. producing satisfactory results in a typicalsmokeless galvanizing operation on thin gauge steel.

The ingredients of a composition of the smokeless blanket flux accordingto my Pat. No. 3,244,551 separately mixed together and heated establisha liquid phase state. This molten flux is then placed on the surface ofa molten galvanizing bath forming What is commonly known as a fluxblanket in a galvanizing pot of the kind described in that patent. Abrightener addition to the galvanizing bath metal consists of analuminum-zinc alloy, comprising about 93% by weight of zinc metal withthe balance being substantially aluminum metal. The galvanizing bath ismaintained at an operating temperature of about 840 F.

This gauge steel sheet as a base metal article is passed through thepreflux wash solution. Before the wash dries, the sheet is fed throughthe flux blanket of the above patented composition into the molten metalgalvanizing bath from whence it emerges through the clear metal. Thesheet steel, as a result thereof, is uniformly coated with thegalvanizing metal and the coating, which is extremely bright and smoothand firmly bonded, is acomplished without the occurrence of any visiblefumes emanating from the bath and with minimum dross formation. Whetherbarium chloride or calcium chloride is used makes no difference in thefinal result.

Having now described the invention, it must be understood that changesand modifications may be made which do not depart from the spirit of theinvention nor from the scope thereof as defined in the appended claims.

I claim:

1. A non-ammoniacal preflux wash composition for preparing the surfaceof ferrous metal articles for galrvanizing completely free of smoke andfumes which consists of about 35% to about 70% by weight of zincchloride, about 5% to about 15% by weight of a material selected fromthe group consisting of boric acid and borax, about 5% to about 10% byweight of potassium aluminum fluoride, about 10% to about 20% by weightof sodium chloride, and about 10% to about 20% by Weight 01fY bariumchloride or calcium chloride or a mixture there- 0 2. A non-ammoniacalpreflux wash as in claim 1 wherein the composition consists of 60% byweight of zinc chloride, 15% by weight of borax, 5% by weight ofpotassium aluminum fluoride, 10% by weight of sodium chloride, and 10%by weight of barium chloride or calcium chloride or a mixture thereof.

3. A non-ammoniacal preflux Wash as in claim 1 wherein the compositionconsists of 60% by weight of zinc chloride, 15% by weight of boric acid,5% by weight of potassium aluminum fluoride, 10% by weight of sodiumchloride, and 10% by weight of barium chloride or calcium chloride or amixture thereof.

4. An aqueous solution of the preflux wash composition as in claim 1with a strength of about 15 to 50 B. at a temperature of around 150 to180 F.

5. An aqueous solution of the preflux Wash composition as in claim 2with a strength of about 15 to 50 B. at a temperature of around 150 to180 F.

(References on following page) 6 References Cited 2,817,894 12/1957Steinberg 148--26 2,867,037 1/ 1959 Lawton 148-26 UNITED STATES PATENTS2 4 Zg L. DEWAYNE RUTLEDGE, Primary Examiner g i fgg 75:94 5 P. D.ROSENBERG, Assistant Examiner Peake 75-94 U-Sl C l XvRl Wasserman 148267594; 11713(); 13442; 252-432

